Well or borehole logging



Jan. 22, 1952 Filed NOV. 12, 1948 LIME SAND

J. J. ARPS WELL OR BOREHOLE LOGGING SHALE (SandMth 44m W 7 W 4 2 SPEETS-SHEET 1 LIME I SAND SHALE N (Lime) permeubie sireuk (Shale) (Sand) \nvenTor Jun Jacob Arps Jan. 22, 1952 J. J. ARPS WELL OR BOREHOLE LOGGING 2 SHEETS-SHEET 2 Filed Nov. 12, 1948 us My Patented Jan. 22, 1952 UNITED STATES PATENT OFFICE Jan Jacob Arps, Tulsa, Okla. Application November 12, 1948; Serial N o 59,656

The present invention relates to Well or bore hole logging and has for its primary object the provisions of new and improved methods and apparatus for obtaining indications of the nature of the earths structure or formation in the vicinity of the bore hole.

Another object of the present invention is the provision of a new and improved method of well or bore hole logging which comprises injecting a contaminating material into the bore hole and thereafter running time spaced instrumental well logs to determine changes in the resulting contamination.

Another object of the present invention resides in the provision of new and improved methods of and apparatus for obtaining indications of the nature of the earths structure or formation in the vicinity of the bore hole by conditioning the hole as by changing the radioactivity of the formations and thereafter observing the decay in radioactivity, as by logging the Well at spaced time intervals.

A further object of the present invention is the provision of new and improved methods of and apparatus for radiologically conditioning or contaminating the earths structure in the viinto the bore hole, the bore hole is then washed rosity, in the vicinity of a bore hole can be determined by radioactive well logging, as by running a gamma ray log of the bore hole. However, known methods require overriding of the natural radioactivity of the earths formations by the injection of mud or other carrier of high radioactivity into the bore hole beforesatisfactory indications can be obtained. This procedure may be dangerous because of the high radioactivity of the mud that must be injected 2 into the bore hole. This difficulty, according to and comparing the results to determine the decay in artificially induced radioactivity and thereby determine the permeability and porosity of the subsurface structure.

A further object of the present invention is to provide a new and improved method of well logging in which radioactive mud is first forced relative amounts of radioactivity and obtaining from them an indication of the formation permeability.

-A;fur.ther object of the present invention is to provide a new and improved method of well logging in which a relatively short lived radioactive tracer is released into the mud, as by generation and as an incident to the drilling and then circulated during the drilling process to contaminate the subsurface structure in the vicinity of the bore hole. Then two time spaced gamma ray logs are run to provide time spaced indications of the change in radioactivity from which the permeability and/or porosity can be determined. I

Another object of the invention is to provide a' new andimproved method of well logging in which radioactive tracer is released into the drilling mud by continuous neutron bombardment.

A further object of the present invention is the provision of new and improved methods for radiologically conditioning or contaminating the earths structure in-the vicinity of the bore hole for the purpose of obtaining indications of the nature ofthe earths formation by bombarding the formations with a neutron emitting substance.

A further object of the present invention is to provide new and improved methods of and apparatus for obtaining indications of the nature of the earths structure orformation in the vicinity of the bore holeby injecting a neutron emitting substance into the formations and theret after logging the hole with aninstrument sensitive to neutrons.

A. further-object of-the present invention resides in the provision of new and improved meth ods for obtainingindications of the nature of the earths structurein the vicinity'of a bore hole by-injecting'into the bore hole a substance that emits neutrons with awvery short half life, waiting for.'.several of these half lives, logging for gamma rays, waiting a period corresponding to several half lives of the expected artificially induced radioactivity and logging again.

Other objects and advantages of the present invention will become apparent from the ensuing description of illustrative embodiments thereof, .in the course of which reference is had to the accompanyingdrawings, in which:

Figshl and 2 are illustrative graphs of time spaced gamma ray logs'run in accordance with the, invention;

" Fig. 3'isa diagrammatic representation of apparatus which can be used in the practice of the invention; and

apparatus made in accordance with the inven- In practicing the present invention, the well or bore hole may be contaminated by forcing radioactive mud into the bore hole. In the event the drilling is carried on with the use of conventional nonradioactive mud, a'method which can be usedis' substantially as follows: "(1) re place the nonradioactive mud with radioactive. mud and force the latter under pressure into the bore hole; (2) wash the bore hole with nQmadiQ; active mud to clean washouts in which radio: active mud may have accumulated dui'ingthe preceding step (this step is not .essential but i s preferably used); (3) run a first gamma ray well log; (4) run a second gamma ray well log after waiting for one or several half lives of the radioactive material; and (5) compare the two. logs. tov determine dissimilarities. and thus. obtain an indication of the formation permeabilityandl porosity.

The. gamma ray well logs may. be standard.

radioactivity logs, see Well Logging by. Radioactivity, .by W. G. Green and/R. Fearon, Geophysics, vol. V, No. 3, 1940,-pp. 272-283, 1. e., the well is explored verticallywith a radiologic measuring instrument sensitive to gamma rays and a curve is plotted on an. automatic. recorder. which is a usual partof the radioactivity logging apparatus.

The radioactive material can be introduced into the bore hole at anyconvenient time. This may be upon completion ofthe drilling operation orafter an interesting zone has-been drilled. When this occurs, the drilling operation is suspended and the above-described method'followed.

The logs indicate the sum of two effects: (1-) the natural radioactivityof the rocks, and (2) the radioactivity due to the infiltration of the radioactive fluid into the rock pores.

The results of an exemplary first log are illustrated in Fig. '1 showing the passage through nine zones, A to I, inclusive, comprising sand, shale and limestone, as indicatedl After the passage of-a predetermined length of-time a secondlogis run. The; resultsof this log are depicted in" Fig. 2. The difierence between the deflections along'the' X axis( horizontal) of the graphs 'of 'Figs. 1 and 2 in'dicat'es the eifect due to th'e' 'contaminati on ofor"the in-' vasion of'the radioactive fluid'z" The difi'erences between the t o grap s; result from the" decay of the artificial contamination, which is present' in the graph of Fig 1, but, which has disappeared from the graph 'of Fig. '2 because of decay. with time;

Considering the graphs in detail, zone. A is interpretable by standard radioactivity log' interpretation as a sand and, since the deflections of the two s are he. same itcl e. pn lhided that no fluid invasioniobkplace and that the sand is nonpermeable. Similarly, zones'B and Hare interpreted as nonpermeablefshale, zones C, E and I as nonpermeable sand, and zoneF as nonpermeable limestone. Marked diiferences are apparent in zoneD, there beingasharp pealg ID to the right in Fig, '1. This indicates angincrease in radioactivity due to penetration of the radioactive, mud into limestone. The zone would, therefore, be interpreted as aporous permeable streak in limestone. appears in zone (3, an, it is, interpretable as, a permeable. streak in sand.

When the radioactive mud is injected into,.the bore hole, acertain amount penetrates 'into' the formations in'the proximity of'theholeT'The, degree of penetration and the amountbf pene'f e ire a e ta. th p mlttPi i-iil a Another peak I 2,

porosity, respectively. As is well known, poresity is expressed by the percentage of the void space in a solid and in the ordinary rocks it is of the order of 20%. Permeability is a function of interconnection between the pore holes. Consequently, it is possible to have material which is porous but not permeable. Such matBria-l will have pore spaces which are not interconnected. As the mud injected into the bore hcleirivades the formation to a certain distance acertainamountof radioactive fluid will be accepted by the formation and this amount is a function of permeability and porosity. The radioactivity of the fluid :accepted by the formation. decays with time andit is this decay that noted.

The radioactive material. used preferably has. An. extremely short life. is impractical because of transportation time a relatively. short life.

from the irradiating plant (atomic pile) to the well location. Cadmium can be used. It

has a gamma radiation of approximately .5,

m. e. v. and half-life of- 43.days. Indium. 114, having a. gamma radiation of -.19. m. e. v. and. a half-life of- 48 days, can also be used. Using materials ot-this character-requires-a wait of four or five months for their activity to decay-sub.- stantially Consequently, a relativelylongperiod of: time is necessary between the two logging operations. However, during thisperiod, the-- well can be completely casedand cemented in conventional manner so tha-t no danger-ofcavein will exist. The cementing and casing-donot prevent the running of thesecond radioactivityground.- A suitable location for generating andrelea sing the tracer would be in "the discharge pipe 'o'f'a pumpnrcmanngthe drilling fluidthrough the bore hole. The discharge pipe can be providedwitli a suitable chamber 1 9, 'as'illustrated in Fig. 5;. Within the chamber are ted electrodes Il -2 and H4 connectedto a u tablesoi t e ove "1 h e t d s r ul t d mi amber ce-mad 'r ac iem 1 ,p splg lsct teliztic ly id i 49 tream y h rr n fl her ec css n ha eae rfiisc e n m penan at eism? i s al, il 783.280 n 55,301 and. as will be described hereinafter. ternati ely. p a atu ke hath w n -FY 1. h chflwi l. e scribed e inafter n which we be s tediniq a hamber. l sepipe .be. a d-.

'Thec sent invention may be used advantageously with methods in which a contaminattaneously viitlrthedrilling as an incide'nt of a, pro ssi'of continuous ra diologic'logging, some whatfirr the nann jer of the methods .andlapparatus disclosedin'my above referred; to, copending applications. In thussimultaneously. drilln d relea in he. fe em ti tracer, is m eria h t n a suitable hal ms;

used. Its half-life is such' tliati-t remains in' the mud and is recirculated with it through the bore hole and thus injected into the *earths formations. The two timespaced gamma ray logs are preferably run so-that the first is obtained immediately after drilling operations have been completed and the second several months thereafter.

An apparatus that may be used is illustrated in Fig. 3. The apparatus here shown is illustrated drilling a well or bore hole 20. The drilling is done in accordance with conventional-rotary drilling practice in which a circulatingfluid, such as a suspension of clay solids in water and conventionally termed rotary mud is usedto carry the drill cuttings out of the bore as the drilling proceeds. The upper portion .of the bore hole is lined with .a surface casing 22 extending, as usual, a comparatively short distance into the hole. A fluid outlet pipe 24 discharging into shale shaker 26 is connected to the upper end of the casing. The shaker separates the formation cuttings carried upward by the drill mud from the drilling mud itself. The latter passes from the shaker 26 to a conventional mud ditch 28 through a radioactivity measuring ,device 30 and a discharge nozzl 32.

Extending into the bore hole through the easing 22 is a conventional hollow drill string designated generally by the reference character 34 which is connected at its lower end to a drill bit 36 having openings 38 adjacent its cutting edges. A Kelly joint 40 is connected to the upper end of the drill pipe and extends through a rotary table 42a mounted on the floor of a derrick. Rotation of the table 42a effects rotation of the Kelly joint 40 and drill string 34 to rotate the bit 36. The upper end of the Kelly joint is connected to the usual rotary hose swivel 42 and the entire drill string assembly is suspended from a traveling block 44 adapted to be raised and lowered in the derrick in conventional manner by means including a cable 46.-

The apparatus for circulating the drilling fluid through the well bore comprises the mud. ditch 28, a settling pit 48, a pump suction pit 50, and a mud pump 52 connected by a suction pipe 54 to the suction pit and by a discharge pipe 56 to the drill pipe.

The volumetric flow of mud flowing through the discharge pipe. 56 may be measured by a fluid meter 58 of conventionaltype. The depth of the well may be measured by any conventional method. This is commonly done by adding together the measurements of lengths of all sections of drill pipe in the well and bysuitable marking of the Kelly to determine how much of it has descended into the well. However, depth measurement can be made by other suitable means, such,for example, as by a depth meter 60 operatively connected by -a measuring line 62 to the traveling block. The meter end of the line is connected to a measuring pulley 64 and the other end passes over pulleys G6 to the traveling block.

.The lower portion of the drill string 34 includes a drill collar 10, a portion of which is covered with an insulated sleeve 12 to the exterior of which are secured a pair of electrodes I4 and 16, which in accordance with my previously referred to copending applications may include cadmium 115 or indium 114 and are adapted to release a radioactive tracer material into the mud stream in quantities indicative of the conduct ilty or resistance of the earth's formation' in the vicinity ofthe electrodes. The electrodes are, as fully disclosed in my copending applications, supplied with, voltage and are made of materials adapted electrolytically to generate and release radioactive material incorporated in one or both of the electrodes. 1

It is apparent from the foregoing that as the drilling progresses the drill collar with its ra-- dioactive releasing electrodes is lowered into the bore hole. Radioactive material is continually emitted into and circulates with the mud stream. In accordance with the present invention,. the radioactive material is not removed from .the mud stream but is recirculated through the bore hole with the result that the earths formation in the vicinity of the bore hole is injected with or invaded by the radioactive substance. The amount of penetration of the formations by radioactive mud is dependent upon the permeability and porosity of the formationaas previously described. With the passage of time and continuous drilling, the walls of the bore hole are more or less permeated with the radioactive material. Then either upon completion of the drilling or whenever desired, a pair of time spaced gamma ray logs as previously described are run in order to ascertain the decay in radioactivity in the time between the two logs. This, as heretofore also indicated, provides information regarding the permeability of the subsurface formations.

If desired, the bore hole can be cleaned of the radioactive material by washing it with a neutral fluid as described in connection with the first described embodiment of the invention. Alternatively, if the half-life of the radioactive material is sufliciently short so as to reduce the radioactivity substantially to zero when the second log is run, the mud can be left in the bore hole.

In the last-described embodiment of the invention it is desirable to include radioactive materials in the electrodes which have a relatively short life. The materials may be cadmium 115 or indium 114, iodine 131, or phosphorus 32.

It may be noted, therefore, that the radioactive tracer may be injected into the bore hole during the process of continuous radiologic logging while drilling and may actually constitute a by-product of that method. The infiltration into the formation takes place right at the bit and before1serious mudding off has taken place, and is, therefore, superior to methods in which radioactive tracer is forced in after a mud cake has formed. The use of short-lived tracers is particularly advantageous because it makes it possible readily to distinguish between the natural radioactive materials which are, by reason of their existence, of very long half-life, and injected tracer material, which has a short life. This difference in half-life provides the necessary means for differentiating between the two types of radioactivity in the time spaced logs.

The mud and bore hole can also be contaminated simultaneously with the drilling by generating a radioactive tracer material in the drill collar by bombardment with neutrons. The neutrons may be derived from a portable source carried in the drill collar and comprising an intimate mixture of about 1 curie of radium salt with about 15 or 20 grams of finely ground beryl- Hum. Other sources of neutrons may be used, such, for example, as any energetic alpha ray emitter mixed with beryllium powder. In Fig. i

there lslllustrated onearrangement. that 'can. be used. It includes' an. artificial radioactive source. that is.maintained-activated continuously by neutron bombardment. It'comprises. a central core 100:- of radium salt and beryllium powder. This core. is surrounded. by paraflimlM. which serves to slow the neutrons to suchzanzexrtent that a. preponderance of .themare vso-called thermal or slow: neutrons, The-outer. surfaeeoi the parafiinis covered. with. a. coating 14 of substance to. be activated and. maintained. activated bycontinuousneutron bombardment. Thissubstance. may be phosphorus. 32 with. gamma; rays of 1.51 m. e. v. and a half-lifeof 12.4 hours; gold 198 having gammarays of..44.m. e. v. and .ahalflife of. 2.7 days; chromium 51. having. gamma: rays of .32 m. e. v.v and. a half-lifeof. .26.5-.days. In accordance with a further feature. of. the invention. the circulating or. drilling mud can: be contaminated with a. neutron emitting. substance.. In this method, neutron emitting materials. are mixed. with the. mud and circulated through. the bore hole. For example. the neutron. emitting substance may be in the form of very small particles each consisting of a neutron emitting core. covered with. aparaffin coating. The neutron. emitting core of. each parti-v cle may comprise radium salt or poloniumqsalt intermixed. with beryllium oxide. Then a. pair of time spaced gamma ray logs are run, preferably: after injection and washing. of the bore hole as in connection with the first described method. In this case the. log corresponding to the contaminated. condition, 1. e., the first of the two logs, indicates a variable which is a function of a: property. of the formation. Theproperty that enters into. the.log it not very definite but can broadly .be described as neutronic. The neutronic rocks can be recognized and thus detected by their ability to. slow down neutrons, capture them, become radioactive and emit gamma rays with acertain energy and. a certain half-life which are characteristic of the rock in question. Correlatablelogs. can be..ob-; tained which willshow theneutronic rocksas a function of depth and can be compared from. well to well giving valuable information regarding the geologicstructureof the subsurface.

Instead of injecting a radioactive tracer. into the bore hole as in connection with the firstofthe-methods described herein, aneutron, emit-t ting substance can be injected into the well. Timed spaced logs with an instrumentsensitive to neutrons are then run. This process is 'ver y similar to the first-described process, except that neutrons are used'entirely.

A substance emitting neutrons-with a very short half-life can be injected into the bore. hole. A time equal-to several of the'haIf-lives of the neutrons is permitted to elapse, after which a gamma ray log is run. After a second period corresponding to several half-lives or the expected artificially induced radioactivity, a second gamma'ray log is run. The-difference between the last two logs is indicativeof the radioactivity artificially induced bythe neutrons.- While difierent embodiments of the'i'nvention have been described,- it should be understood" that various modifications may be-made therein which are within the true spirit and scope of the invention as defined in the following claims.

What is claimed is: v 1. A method of logging a borehole or well which includes injecting into the bore hole-aneutron emitting substance capable of contain-- like ijl

mating. the earth's. formation in the vicinityof the hole, andthereafter running a pair of neutron. responsive logs. spaced in time relative to the injection. to obtain information regarding characteristics of the: earths formation.

2. A method of logging a bore hole or well which includes circulating mud containing a neutron emitting substance under pressure into thev borehole, washing the bore hole with neutral: mud, running. a' first neutron responsive well. l'og, waiting a time .interval, running. a second neutron: responsive welllog,. and comparing the two logs' to obtain information regarding characteristics. of the earths formation in the regions of the-bore hole.

3. A method of logging abore hole or well which includes circulating mud containing a neutron emitting substance under pressure into the bore hole, washing the bore hole with neutral mud, running a first gamma ray well log, waiting a time interval, running a second gam-. ma ray well log, and comparing the two legs to obtain information regarding characteristics of the earths formationin the regionsof the bore hole.

4. A method of logging a. bore hole or well which includesmixing a neutron emitting sub stance with the fluid introduced. into the .bore hole; and thereafter running a gamma ray well log of thebore hole.

5. A method of. logging a bore hole or well which includestmixing with the bore hole fluid a neutron emittingsubstance capable of contaminating .the penetrated formations surrounding the bore hole; permitting the neutron emitting substance to contaminate the said penetrated formations from said fluid; and thereafter running agamma ray log of the'bore hole to obtain thereby ameasure of the gamma ray radioactivity induced by said neutron emitting substance in said formations.

6. A. method of logging a borehole or well which includes mixing with the borehole fluid a neutron emitting substance capable of contaminating the penetrated formations surround ing'the borehole; and thereafter running a first gamma-ray. log. of the bore hole; permitting a time interval ofv at least one half-life of the neutron emitting substance to lapse following said first gamma ray log; and then running a second gamma ray log. of the borehole, thereby to obtain the difi'erence between the gamma ray radioactivities of the first and second gamma ray logs, as a measure indicative of the radicactivity artificially induced inthe materials ofsaid contaminated penetrated formations.

7. A method of logging a bore hole or well which includes mixing a neutron emitting sub-- stance with the-fluid introduced into the bore hole; and thereafter running. a plurality of time spaced gamma ray measurements in the bore hole.

JAN JACOB ARPS.

REFERENCES CITED Theifollowingreferences are or record in the file 'of'this patent:

UNITED STATES PATENTS- Number Name Date 2,339,129- Albertson Jan. 11, 1944 2,358,945 Teichman Sept. 26', 1944 23645975 HeigI'et'aI. Dec. 12, 1944 2,385,378 Piety Sept. 25, 1945 2,390,931 F'earon Dec. 11, 1945 

